Lenticular display device

ABSTRACT

A lenticular display device comprises a back panel  2  having a major surface  15  with a substantially fixed curvature. A front panel  4  is substantially in register with the back panel and is releasably pressed against and into conformity with the major surface  15  by cams  11  which apply oppositely-directed tangential forces at the edges of the front panel. An image sheet  20  and lenticular lens  21  are sandwiched between the two panels, the lens being maintained in intimate contact with substantially the entire area of the image sheet by the panels. In another embodiment the front panel is omitted and the lens itself serves as the front panel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application of PCT Application No.PCT/IE02/00052, filed on Apr. 23, 2002, and claims the benefit of IEApplication No. S2001/0404, filed on Apr. 24, 2001, and also claims thebenefit of IE Application No. S2001/0480, filed on May 17, 2001.

The present invention relates to a display device, and in particular, toa device for displaying a removable image through a lenticular lens.

Typically, a lenticular lens is mounted in a light box or in a frameworkwithout a light box. A sheet of paper or other suitable medium havingtwo or more interlaced images printed thereon is laminated to the backof the lenticular lens. Accordingly, when the images are viewed throughthe lenticular lens depending on the angle at which the subject is tothe lens one or other of the images is visible. As the subject movesposition relative to the device the image viewed repeatedly changes fromone image to the other. When the lenticular lens is mounted in a lightbox the interlaced images printed on the lenticular lens are translucentand light passes from the rear through the image and lens forilluminating the image. When a light box is not provided the image isilluminated from the viewing side through the lenticular lens, and theinterlaced images are opaque.

Lenticular lenses have a series of lenslets which have a focal point onthe rear flat side of the lens. Therefore the lenses are designed tohave the image firmly adhered to the rear of the lens. A gap between thelens and the image will result in the image being out of focus resultingin increased ghosting or crosstalk, the larger the gap the moreghosting. It is therefore important to have intimate contact between thelens and image for high quality images. To date the most commonly knownmethods of achieving this are by adhering the image to the lens, whichis expensive and time consuming, or by direct printing which requiresexpert knowledge.

Lenticular displays have many advantages; for example, they permit twoor more images to be displayed from the one site simultaneously, andadditionally they allow the display of images in three dimensions, forexample, by displaying a foreground, middle ground and distant ground.However, if a large or fine lenticular image is required the image hasto be permanently laminated or printed to the rear of the lens whichresults in a new lens being required for every image change, thelaminating of the images generally requiring expensive expertise andequipment.

Existing devices for replacably mounting an image behind a lenticularscreen and movable displays are known. Patents GB2206227, U.S. Pat. No.5,146,703 and GB2308005 describe such devices. These devices havelimited use as they do not allow for large images to be viewed nor dothey allow for high resolution images to be viewed at any significantsize. They are also bulky and expensive to manufacture. These attemptsrely on tightly sandwiching the image and lens between two planarmembers, so as to maximise the contact between the rear of the lens andthe image, this method requires the use of thick rigid transparent glassor plastic in front of the lens, extremely rigid surface behind theimage and many fixings to provide the required clamping force. The lensrequired for this method is generally a thick, coarse pitched, expensivelens which is more forgiving with air gaps. The reason for this is thatas an air gap behind a thick lens would result in a smaller percentageerror on the position of the image with respect to the focal point ofthe lens than a thin lens with the same size air gap, thick lensestherefore reduce the negative effect of any gaps between the lens andimage. This clamping method is of limited success as it is impossible tocompletely eliminate gaps between image and lens without usingimpracticably thick sandwiching members and very high clamping forces,the problem being accentuated as the image size and therefore thesurface area increases so that any image over typically over A3 is notof acceptable standard. The thickness of the sandwiching members is suchso as to render such a device expensive, heavy and impractical. Acompany called Benchmark Imaging in the U.S.A. have a product whichemploys a vacuum between a front and rear panel to hold the image andlens into close contact. A camming mechanism moves the image and lensrelative to each other. This system is supplied with an image and doesnot allow for changing of the image by a casual user. It is also limitedto a lens pitch of 15 lpi which is coarse and its maximum size is 4feet×4 feet. A major disadvantage is that the image has to be changed inthe factory, therefore making it impractical for sites which needregular updating.

There is therefore a need for a display device, which is not limited indisplay size or lens pitch for displaying stationary and movinglenticular images and which allows for a lenticular lens to be reusedindefinitely. There is also a need for such a device which allows forquick and easy changing of the images as required by an unskilledoperator.

The present invention is directed towards providing such a device.

According to the invention there is provided a display device comprisinga first panel having a major surface with a substantially fixedcurvature, a second panel substantially in register with the first paneland releasably pressed against and into conformity with the said majorsurface by means applying oppositely-directed tangential forces at theedges of the second panel, and an image sheet sandwiched between thefirst and second panels, wherein either the device includes a lenticularlens also sandwiched between the panels next to the image sheet or oneof the panels is itself a lenticular lens, in either case the lens beingmaintained in intimate contact with substantially the entire area of theimage sheet.

The invention will be more clearly understood from the followingdescription of embodiments thereof which are given by way of exampleonly with reference to the accompanying drawings in which:

FIG. 1 is a perspective view a device according to the invention.

FIG. 2 is a end view of the device of FIG. 1 showing the curved shape ofthe device.

FIG. 3 is a rear view of FIG. 1 showing the tensioning and retainingmeans.

FIG. 4 is a exploded perspective view of FIG. 1.

FIG. 5 is another exploded perspective view of the device of FIG. 1.

FIG. 6 is perspective view of a second embodiment of the device, withtensioning cams mounted onto the rear panel tensioning the front panel;a rib which does not increase the chord height is also shown.

FIG. 7 is an end view of FIG. 6 showing the spacing means between thefront panel and back panel.

FIG. 8 is another perspective view of FIG. 6 with the front panelremoved.

FIG. 9 is the same view as FIG. 8 with the lens removed.

FIG. 10 is the same as FIG. 6 with the lens and image sheet removed.

FIG. 11 is an exploded view of FIG. 6 showing the insertion of a newimage sheet.

FIG. 12 is a perspective view of a third embodiment similar to thedevice of FIG. 6 but showing an alternative means for aligning the lensand image sheet with respect to each other, the front panel beingremoved.

FIG. 12 a is as FIG. 13 but with the lens removed.

FIG. 13 is perspective view of a fourth embodiment of the inventionwhere the image sheet is moved with respect to the lens with the frontpanel and lens removed.

FIG. 14 is a plan view of FIG. 13.

FIG. 15 is a perspective view of FIG. 13.

FIG. 16 is a view similar to FIG. 13 but including the lens.

FIG. 16 a is a close-up of the cam and mounting arrangement of FIG. 16.

FIG. 17 is a perspective view of FIG. 13 with the front panel and lensin position.

FIG. 17 a is a rear view of the device of FIG. 17 showing the lowprofile ribs.

FIG. 18 is a perspective view of a fifth embodiment of the invention.

FIG. 19 is a exploded view of FIG. 18.

FIG. 20 is an end view of FIG. 18.

Referring to the drawings and initially to FIGS. 1 to 5 there isillustrated a lenticular display device according to a first embodimentof the invention indicated generally by the reference numeral 1. Thedevice 1 comprises a rectangular back panel 2 of semi-rigid materialattached to rigid, curved members 3 a and 3 b by bolts not shown, thuspresenting a major surface 15 which is convex in a plane normal to theopposite parallel side edges 8, 60 of the back panel. Although the backpanel 2 per se is semi-rigid, the rigid members 3 a, 3 b maintain thecurvature of the back panel substantially fixed. A transparent, flexiblerectangular front panel 4 is substantially in register with the backpanel 2 and is secured at one edge by bolts 5 to a first, generallyU-shaped cross-section retaining means 6. The first retaining means 6has a channel 7, an internal surface 22 of which bears against the edge8 of the back panel 2.

Located at the opposite edge of the front panel 4 is a further retainingmeans 9 which includes a series of rotary cams 11 with retaining flanges40, the cams 11 being used to tension the front panel 4 across the backpanel 2 as will be described. The cams 11 are mounted to the front panel4 using bolts 30 and are rotatable about axes normal to the panel 4. Thecams 11 have generally egg-shaped cam surfaces which bear upon the edge60 of the back panel 2, each cam surface having diametrically oppositecam surface regions 12 and 13 respectively further and nearer to the camaxis. The retaining flange 40 engages the rear surface 14 of the backpanel 2 thus retaining the front panel 4 a set distance from the backpanel 2. The retaining means 6 also has a series of bolts 16 in threadedholes 17 located in the outside wall 42 of the retaining means 6, thebolts 16 engaging with the edge 8 of the back panel 2. The position ofthe bolts 16 further determines the tension in the front panel 4, aswill be described.

Sandwiched between the back panel 2 and the front panel 4 are an imagesheet 20 and a lenticular lens 21. The image sheet 20 is against theconvex surface 15 of the back panel 2 with its printed surface beingviewable through the front panel 4. The lens 21 is positioned with itsflat surface 50 against the image sheet 20 and behind the front panel 4.The image sheet and lens are preferably of material with a similarthermal coefficient of expansion to allow for thermal expansion whenused in outdoor areas. The lens, back panel and front panel are ofsemi-rigid material such as Perspex, polycarbonate or the like. Thethickness of the materials are such so as to provide sufficient strengthand rigidity so as to eliminate gaps as required and avoid excessivecreep due to tension or compression.

The rotary position of the cams 11 is determined by the rotation of thebolts 30. The bolts 30 run through the retainer 9 and holes 51 in thefront panel 4 thereby securing the cams 11 relative to the edge of thefront panel 4. When the cams 11 are rotated to bring the surface regions12 to bear against the edge 60 of the back panel 2 the front panel 4 isunder maximum tension. It will be appreciated that such tension arisesdue to the opposite, mutually outwardly-directed tangential forcesexerted on the front panel 4 by the retaining means 6 and 9 which arebiased apart by the cams 11. In the position of maximum tension the lens21 and image sheet 20 are tightly pressed between the back panel 2 andfront panel 4 thus substantially eliminating gaps between the imagesheet 20 and lens 21. The contact force between the lens 21 and imagesheet 20 is such that the image sheet 20 and lens 21 are firmly pressedagainst each other so that the lens is maintained in intimate contactwith substantially the entire area of the image sheet. Preferably thecurve induced in the lens is of a constant radius. The radius is of sucha value so as to preferably minimise the chord height of the devicewhile still performing its function.

When the cams 11 are rotated so that the cam surface regions 12 aredisengaged from the edge 60 the tension is reduced, the further the cams11 are rotated from this position the less tension is present in thefront panel 4. When the cams 11 are rotated so as to provide maximumtension as described above the retaining flange 40 of the cams 11 engagewith the rear surface 14 of the back panel 2 thereby retaining the frontpanel 4 close to the back panel with a set gap between the front panel 4and back panel 2. FIGS. 2 and 3 show the surface 12 of the cams 11engaging with the edge 60 of the back panel 2.

In use, the cams 11 are rotated so as to remove the tension from thefront panel 4, further rotating the cams 11 until the retaining flanges40 are no longer in contact with the rear surface 14 of the back panel2, releasing the front panel 4 and allowing a new image sheet 20 to beinserted between the lens 21 and back panel 2. Once inserted the frontpanel 4 is brought into close engagement with the lens 21 which iscorrespondingly brought into close abutment with the image sheet 20which is effectively sandwiched between the front panel 4 and back panel2. The cams 11 are then slightly rotated so as the surface 13 is incontact with the edge 60 of the back panel 2 and the flange 40 holds thefront panel 4 in place against the lens 21. There is slight tension inthe front panel 4 which allows the image sheet 20 and lens 21 to bealigned so as to provide proper lenticular functionality. Once properalignment has been achieved the cams 11 are then fully rotated so thatthe cam surface 12 is in direct contact with the edge 60 of the backpanel 2. The front panel 4 is therefore under high tension thuseliminating the gaps as described before, allowing for a high qualitylenticular image. The tension in the front panel and stiffness in theback panel resulting in such pressure between the lens and image sheetthat the image sheet remains stable when the front panel is firmlypressed on, the tension is also such that the image sheet 20 and lens 21are securely held in place and will not move relative to each otherunder normal circumstances until the tension is removed. The image sheetis provided in conventional manner with two or more interlaced imageswhich are viewable through the lenticular lens 21.

If the tension in the front panel 4 is inadequate for reasons ofmaterial creep in the front panel 4 over a period, its tension may beincreased by tightening the screws 16 on the retaining means 6 or bymeans of tensioning springs (not shown). Stiffness is added to the freeedges 8, 60 of the back panel 2 by the rigid retaining means 6 and 9which help the back panel 2 to maintain a straight edge.

A second embodiment of the invention is shown in FIGS. 6 to 11. In thisembodiment the cams 200 are mounted on the rear panel 2 and rotated soas to tension the front panel 4 through outwardly-directed tangentialforces applied at its opposite edges. The cams have retaining flanges205 which engage with the front surface 207 of the front panel 4 andhold it in close engagement with the lens 21. The free edges 208 of theback panel 2 have stiffening and spacing means 209 provided so as tocontrol the straightness of the free edges 208 over their length and toensure that the gap 210 between the front panel 4 and back panel 2 isthe sum of the thickness of the image sheet 20 and lens 21 so as toensure that when in tension the front panel 4 will engage the lens 21over it's entire surface without the need for excessive tension. Ribs300 a and 300 b create the curve for the back panel. The design of theribs 300 allow the device 1 to have a minimised chord height.

FIG. 6 shows the cams 200 engaged with the front panel 4. The cams 200protrude through respective openings 203 in the front panel 4 near itsedge and the camming surface 228 engages the surface 227 of the opening203 when rotated so as to tension the front panel 4. The cams 200 have aslot 204 to allow them to be easily turned by screwdriver so as toengage and disengage with the front panel 4. Referring now to FIGS. 7, 8and 11, when engaged the retaining flanges 205 retain the back surface211 of the front panel 4 against the surface 212 of the spacing means209, therefore maintaining the required gap 210. Should the gap 210 begreater or less than the cumulative thickness of the image sheet 20 andlens 21 the lens and image sheet would not have firm contact towards thesides 213 of the device, the area of the low contact are depending onthe size of the gap 210.

FIG. 8. shows the image sheet 20 and lens 21 positioned relative to eachother. The image sheet 20 has the interlaced image strips exactlyperpendicular to the bottom edge 220 (FIG. 9) of the image sheet 20. Thelens also has an edge 221 which is cut exactly perpendicular to thedirection of the lenslets. The lens 21 and image sheet 20 are insertedbetween the front panel 4 and the back panel 2 with their correspondingedges 221 and 220 resting on the flat surface 223 provided by the rib224 as shown in FIGS. 9 and 10.

In use the cams 200 are rotated to release the front panel 4. The imagesheet 20 is replaced with a new image sheet which is placed as beforebetween the lens 21 and back panel 2. The front panel 4 is thentensioned by rotating the cams 200 with a screwdriver so as to engagethe cam surface 228 with the surface 227 of the opening 203 in the frontpanel 4. The top edges 225 and 226 of the corresponding image sheet 20and lens 21 are pushed down so as to engage their opposite edges 220 and221 with the flat surface 223 of the rib 224. With the edges 221, 220and the surface 223 in contact the lens and image sheet are in perfectalignment.

Referring now to FIGS. 12 and 12 a, a third embodiment is essentiallythe same as the second embodiment but uses a different technique foraligning the image sheet 20 and lens 21. At each opposite side edge theimage sheet 20 and lens 21 are provided with registering, elongatedslots 240 and 241 respectively. The flat (elongated) edges 242 of theslots 240, 241 are perpendicular to the direction of the lenslets. Boththe image sheet 20 and lens 21 are located on pins 250, each pin 250being a nominal fit with a respective pair of registering slots 240, 241so that the interlaced images and the lenticules remain parallel to eachother while allowing for relative movement in a direction perpendicularto the lenslets. In use both image sheet 20 and lens 21 are insertedbehind the front panel when the cams 200 are disengaged, the image sheet20 and lens 21 are mounted on the pins 250 thus aligning the lens 21 andimage sheet 20, the front panel 4 is then positioned so the cams 200 areprotruding through the opening 203 on the front panel 4. The front panel4 is then tensioned as before.

Either of these methods allow for simple installation of a new imagesheet into the device ensuring correct alignment.

Referring now to FIGS. 13 to 17 a there is shown a fourth embodimentwhere the image sheet 20 moves relative to the lens 21. The image sheet20 and lens 21 are mounted on the pins 250 as previously described.FIGS. 16 and 16 a show how the lens is located with the slot 241 locatedon the pin 250 as described in the previous embodiment, and a hole 275in the lens 21 located on the opposite pin 250. The lens 21 is thusaligned with the image sheet 20 as before but fixed due to the pin 250and hole 275 arrangement. The slots 240 in the image sheet 20 allow theimage sheet to move relative to the lens 21 in a direction perpendicularto the lenslets. To each side of the image sheet is located a rotary cam270 and 271, the position of the cams 270 and 271 determining theposition of the image sheet with respect to the lens. The cams 270 and271 always being out of phase with each other so as not to oppose eachother.

In use the image sheet 20 is mounted on the pins 250 between the cams270 and 271. The lens 21 is also mounted on the pins 250, with the hole275 engaging the corresponding pin 250, thus preventing the lens frommoving. Both image sheet 20 and lens 21 are thus aligned and the frontpanel 4 positioned as in the third embodiment. To move the image sheetrelative to the lens cam 271 is rotated by motorised means so as toengage the edge 273 of the image sheet 20 causing it to move withrespect to the lens 21 in a direction perpendicular to the lensletsdirection. A stationary viewer is thus presented with a moving image.After a period of time the cam 271 is disengaged and opposite cam 270 isengaged so as to engage edge 272 and return the image sheet 20 to it'sstarting position. This cycle is repeated as required. The movement ofthe cams 270 and 271 is determined by controlling means (not shown).

An adjusting means (not shown) may be provided on the pin 250 or lens 21so as to allow the lens to be positioned with respect to the image sheetso as to be able to determine which image is viewable at the start orend of a cycle.

In this fourth embodiment, while the image sheet 20 is shown as movingrelative to the lens 21 it will be appreciated that the opposite may betrue, i.e. the image sheet could be fixed and the lens moved relative toit. Also while the cams 270 and 271 are shown as being of simpleelliptical shape it will be appreciated that their profile may vary.Also, although two cams 270 and 271 are shown it will be appreciatedthat any sort of actuator may be used.

Referring now to FIGS. 18 to 20, there is shown an fifth embodiment ofthe invention. This embodiment is in effect a reversal of thearrangement of the first embodiment. In this embodiment the front panel100 is of a substantially fixed curvature and a flexible back panel 101is forced into engagement with the lens and image sheet which aresandwiched between the two panels. In particular, the back panel 101 ismaintained under compression, through the application of mutuallyinwardly-directed tangential forces applied at its edges, to press theimage sheet 102 and the lens 103 against the concave rear surface of thefront panel 100 so that the lens is maintained in intimate contact withsubstantially the entire area of the image sheet. The lens 103 is placedwith lenslets facing the convex surface 104 of the front panel 100. Theimage sheet 102 is placed image side 105 against the flat side 106 ofthe lens 103. Behind the image sheet 102 is placed a separator 107, andfinally the back panel 101 is placed behind the separator 107. Securelyconnected to opposite sides of the front panel 100 is a pair ofgenerally U-cross section retaining members 109. The retaining members109 having a channel 110 to nominally accommodate the thickness of thefront panel 100, back panel 101, image sheet 102, lens 103 and separator107. The spacing apart of the retaining members 109 along thecircumference of the front panel 100 and the length of the back panel108 are chosen so as to slightly compress the back panel 108 so as itforms a concave shape and compresses the lens 103 and poster 102 betweenthe separator 107 and front panel 100.

The tensioning means in this embodiment is provided by forcing the backpanel 101 between the retaining members 109 which have a circumferencelength nominally shorter than the length of the edge 110 of back panel101. Alternatively cams or other compressing means may be employed as inthe first embodiment so as to compress the back panel 101 when it is inposition.

The separator 107 avoids any friction between the poster 102 and theback panel 101 therefore ensuring the poster position is not changedwith the insertion of the back panel 101. The image sheet 102 and lens103 may be aligned as in the third embodiment. The tension between theimage sheet and lens should also meet the requirements of the firstembodiment as previously stated.

Various modifications to the embodiments are possible.

For example, although cams are used to tension the front panel in thefirst four embodiments, it will be appreciated that other tensioningmeans may be used. In particular it is possible to use springs incompression or tension at one or both edges of the panels to apply thenecessary tangential forces. Springs may also be used to compress therear panel in the fifth embodiment. In all cases it is also possible touse other devices such as adjustable bolts, wedges or elastic materialsin compression or tension.

Also while in the first four embodiments the front panel 4 has beenshown as the member under tension it will be appreciated that the lens21 may be under direct tension eliminating the requirement for a frontpanel 4; i.e. the lens 21 may itself constitute the front panel.Similarly, in the fifth embodiment the flexible back panel could beeliminated and the lens be placed under direct compression and serve asthe back panel. The image would then be viewed from the rear. Ingeneral, any of the described embodiments could be modified to eliminateeither one of the panels and use the lens to serve directly as theeliminated panel.

While the image sheet 20 is generally described as being viewablethrough the front panel 4 it may alternatively be viewed through theback panel 2. Where this is so the ribs 300 (in the embodiments wherethey are present) may be on the opposite side to the viewing side.

While the back panel 2, where it is the fixed curvature panel, isdescribed as being curved by ribs it will be appreciated that the backpanel 2 may be pre-formed into this shape. The curve in the back panel 2may also be induced by attaching it to a second curved panel. The curvemay also be induced by forcing and retaining both straight edges 8 and60 of the back panel 2 towards each other. In an alternative embodimentof the invention the curve may be induced in the back panel 2 by theside walls of a frame or light box. Also, where curved ribs are used, itwill be appreciated that more may be employed; indeed a rib oftransparent material may be added in between the ribs described so as toreduce any negative effect on the viewable image when backlighting isemployed. Similar considerations to the above apply to the front panelin embodiments where that is the fixed-curvature panel.

The back panel 2 may be of transparent or translucent material and theimage sheet of translucent material to allow a light source toilluminate the images from the rear. Alternatively, it will beappreciated that it may alternatively be of an opaque material such asaluminium which has the advantage of being light. To compensate for thelack of transparency thin backlight such as Rexams electroluminescentmaterial may be employed to backlight the image where required.

Also while two actuators are shown, on opposite sides of the movingimage sheet one actuator may only be employed with a automatic returningmechanism on the opposite side such as a spring.

While the lens 21 is shown as having it's lenslets parallel to thestraight side edges of the back panel it will be appreciated that thelenslets may be orientated perpendicular to the straight edges with, inthe case of the fourth embodiment, the cams 270 and 271 correspondinglypositioned so as to move the image sheet parallel to the lensletsdirection.

In the third and fourth embodiments of the invention, while the lens 20is held in a particular position by the pin 250 it will be appreciatedthat other means may be employed such as edge contact against thespacers 209 or indeed a movable stop which may position the lens 21 withrespect to the image sheet 20 to determine which particular image may beinitially seen from a particular viewing angle, or in the case of thefourth embodiment which image is first seen from a particular viewingangle. While a certain arrangement of slots and locating pins are shownfor aligning the lens 21 and image sheet 20 it will be appreciated thatany number of slots may be used, and the may not necessarily be placedon opposite edges.

While the image sheet 20 is shown as a single part it may be mounted orlaminated to achieve the required stiffness. Where this is employed, theimage sheet will be considered to include the mounting substrate and thethickness of the image sheet will be the total thickness of thelaminate.

The advantages of the invention are many:

a. By virtue of the construction of the display device the image sheetcan readily be removed and replaced with an alternative image sheethaving different images thereon eliminating the need for expensive andtime consuming laminating and the requirement for a new lens for everynew image sheet. For the price of a normal print the image sheet can bechanged.

b. Insertion of the image sheet is simple and quick.

c. The simple guide design used in the embodiments allows for thethermal expansion of the lens ensuring continual free movement.

d. The invention makes lenticular technology more affordable for repeatusers of lenticular images.

e. The invention allows large properly prepared image sheets to bequickly changed by an unskilled operator.

f. The lens is held in intimate engagement with the image sheet whichallows for large images using finer pitch lenses than was previouslypossible with similar devices. The finer pitch lens allows higherresolution and more frames to be displayed which is essential for goodanimation, zoom and morph effects. The finer pitch lens also allows forsmaller text size.

g. The lens is reusable, therefore reducing the cost of production forlenticular images

h. The device may be permanently situated in say a bus shelter allowingfor a permanent “lenticular” site which may have multiple image changesat a low cost.

i. The device as described in the embodiments prevents warping of thelens which is a common problem in hot climates.

j. Where two panels are used the device protects the lens from physicaldamage.

k. The device is compact.

l. In one embodiment the device also allows for stationary viewing ofthe lenticular image by moving the lens relative to the image sheet.

m. The device is economic to manufacture light and requires littlemaintenance.

n. A thin, cheaper lens may be employed than could be used in othersystems.

The invention is not limited to the embodiments hereinbefore describedwhich may be varied in construction and detail.

1. A display device comprising a first panel having a major surface witha substantially fixed curvature, a second panel substantially inregister with the first panel and releasably pressed against and intoconformity with the said major surface by means applying simultaneousoppositely-directed tangential forces at respective opposite edges ofthe second panel, and an image sheet sandwiched between the first andsecond panels, wherein either the device includes a lenticular lens alsosandwiched between the panels next to the image sheet or one of thepanels is itself a lenticular lens, in either case the lens beingmaintained in intimate contact with substantially the entire area of theimage sheet.
 2. A device as claimed in claim 1, wherein the majorsurface is convex and the tangential forces are directed away from oneanother to place the second panel under tension.
 3. A device as claimedin claim 1, wherein the major surface is concave and the tangentialforces are directed towards one another to place the second panel undercompression.
 4. A device as claimed in claim 1, wherein theforce-applying means comprises at least one rotary cam mounted at oneedge of one panel and bearing on or adjacent an edge of the other panel.5. A device as claimed in claim 1, wherein the force-applying meanscomprises at least one spring at the edge of the panels.
 6. A device asclaimed in claim 1, wherein one of the image sheet and lens is mountedfor reciprocation relative to the other.
 7. A device as claimed in claim1, further including spacing means for maintaining opposite edges of thefirst and second panels apart by a gap which is substantially the sum ofthe thicknesses of the image sheet and lens.